The subject matter of this invention relates generally to programmable controllers, and the programming panels therefor, especially in relationship to the contact entry sequence.
Relay logic ladders include "rungs" of interconnected switches, relay contacts and output devices (such as relay coils) disposed in rows between two conductors of a power supply for using the principles of relay logic for controlling electromechanical devices. Using art in existence prior to the advent of relay line solver technology, relays, switches and other devices of the logic ladders are hard-wired and relatively large electromechanical devices which are strung together between the conductors of a power supply. The various switches and contacts of the relay logic ladder are in various states of conduction or non-conduction depending upon the disposition of mechanical devices such as floats or depending upon the disposition of output devices such as relay coils to which they are interlinked electrically or mechanically. In the event that appropriate contacts or switches are in a closed state in a given "rung" of the ladder, the output device, usually a relay coil, controlled by the "rung" will be actuated. The actuation may cause certain actions external or internal to the relay ladder to occur.
With the advent of computer technology, the relay ladder diagram, which is a graphical representation of the relay ladder, is simulated within a programmable controller. This eliminates the bulky, relatively expensive relays, saves space, and generally reduces the need for expensive hard-wired interconnections. The "programmable" portion of the controller gives the controller operator or logic system designer flexibility. Aternately, the various interconnections between contacts, switches and output devices in a relay rung can be simulated with a diode matrix, as is taught in U.S. Pat. No. 3,950,736, issued Apr. 13, 1976 to Dix et al. Essentially, this requires the use of a diode matrix which can be programmed by moving diodes into and out of the matrix in a predetermined fashion. One disadvantage of this is the relatively cumbersome arrangement of the diode matrix and the level of dexterity and skill required in using or "programming" it. With the computer controlled ladder diagram solver (sometimes called a line solver), a programming panel is used for initially programming or for subsequently changing the status of various memories contained therein. As the prior art developed, it is suggested that certain characteristics began to emerge as important. They are: complexity of the problem to be solved; memory efficiency; and operator skill. Complexity of the problem to be solved is associated primarily with the arrangement of the interconnections between elements in a rung of a ladder diagram and, to a lesser extent, with the number of elements in a rung of a ladder diagram. Memory efficiency is associated with the number of memory bits or locations required for complete entry of a rung of a ladder diagram into the programmable line solver. Operator skill is associated with the operator's capability to convert the symbol of a rung of a ladder into manipulations of the programming panel (or program loader) of the programmable controller with speed and a minimum potential for error. An examination of the prior art shows that the attainment of all three important features in a single programmable controller is difficult. Consequently, the prior art seems to branch in two directions--the choice of which depends upon which of the aforementioned important functions is to be optimized at the expense of the others. In one case, optimization tends towards flexibility--that is, the programmable controller is designed and constructed so that relatively complex ladder diagrams can be entered into the programmable controller for solution thereby at the expense of memory efficiency. One of the problems associated with memory requirement lies in the fact that in most of the prior art of the aforementioned kind, separate memory words must be utilized for entering elements and for entering the interconnections between elements in a complex ladder diagram. Corollary to this, is that additional operator manipulation of the programming panel must be made by the operator to place the additional interconnection information into the memory. Examples of the preceding may be found in U.S. Pat. No. 4,021,783, issued May 3, 1977 to G. C. Highberger and entitled "PROGRAMMABLE CONTROLLER". A further example is found in the Allen-Bradley Company Bulletin No. 1774, entitled "PLC PROGRAMMING AND OPERATION". Still a further example is found in a bulletin from Industrial Solid State Controls, Inc. dated 1/73 entitled "IPC.TM. INDUSTRIAL PROGRAMMABLE CONTROLLER MEMORY LOADER/MONITOR (L/M)". Still another example is found in U.S. Pat. No. 3,686,639 issued Aug. 26, 1972 to Fletcher et al and entitled "DIGITAL COMPUTER-INDUSTRIAL CONTROLLER SYSTEM AND APPARATUS". Another example is found in a SQUARE D COMPANY bulletin dated Jan. 2, 1975, identified by the following: "Cl.8881 PROGRAMMABLE CONTROLLER PROGRAM BOX--APPLICATION OF TYPE PR-2 PROGRAM BOX". Another example is found in apparatus described in a manual provided by the MODICON Company entitled "484 MANUAL, MARCH 1978" (for example, pp III-1 through III-32 and A-1 through A-20). In the other case, the trend appears to be towards memory efficiency at the expense of flexibility. This type of controller or processor tends to be limited as to the number of elements which can be entered, the number of possible circuit combinations which can be utilized and/or the total length or size of the ladder rung. An example of this is found in apparatus described in a manual provided by the MODICON Company entitled "MODICON 184/384 MANUAL", June 1977 (for example, pp 31-65 and A-2 through A-5). Furthermore, apparatus has been found in which some contact and associated interconnection information may be entered into one word of memory in a limited case with one key manipulation of a single key of the program panel. Such may be found in General Electric Company descriptive bulletin dated 1/77, entitled "LOGITROL CONTROL". However, in no case discovered can the entire ladder diagram rung be entered in this way, i.e. with all interconnections entered by use of a contact entry device or key. Regardless of which trend is followed in the prior art, some form of operator skill is required. Generally, the operator must be able to determine the sequence in which to enter the various contacts and a coil. The decision making process involved therewith provides an opportunity for mistake. It would be advantageous therefore if means could be found for determining the sequence of contact entry based on previously entered contact information so that the operator could be alerted as to which contact to enter next each time a previous entry operation is completed.